Positive flow cut off of a filling apparatus is difficult to achieve in sanitary valves, especially when viscous fluids are being dispensed which have a tendency to leave tailings that cling to the dispenser nozzle after a dispensing cycle. For example, when running hot process cheese at 160 to 180 degrees Fahrenheit, it is difficult to achieve positive flow cutoff in a filling apparatus using conventional sanitary filling valves. Upon full closure of a dispensing valve, residual cheese tends to adhere to external valve surfaces. This retention can lead to unacceptable variability in weight control for the packaged cheese. In addition, the residue can become dislodged at a later time, and possibly drip or otherwise drop onto an underlying conveyor belt or other surfaces. Removal of the drip or tailing residues from the nozzle by mechanical or manual means is generally difficult or overly burdensome in practice.
The prior art reflects a number of different approaches to preventing build-up of residue of dispensed material on dispenser nozzles. U.S. Pat. Nos. 5,309,958; 4,970,985; 4,350,187; 3,926,229, and Japanese published appln. nos. all generally describe a dispensing apparatus including means for removing tailings and the like by which air or a gas is blown out of a hole or array of gas passageways provided in the dispensing head itself. However, these approaches require fundamental design changes in the dispenser head or filling valve construction. It would be highly desirable to solve the tailings problem in a manner which can be implemented on existing dispensing head equipment with little modification or retrofitting required on the dispenser head, especially with respect to the wetted parts of the dispenser head.
U.S. Pat. Nos. 5,226,565 and 5,447,254 describe nozzle attachments or fittings for dispensers for use in nozzle cleaning or shut-off drip protection. Both patents provide air passageways that direct air at the discharge end of a nozzle in which the air passageway is partly defined by dispenser head components and not the nozzle attachment exclusively. The attachment of the nozzle attachment and detachment requires the use of tools and the attachment uses wetted parts of the nozzle in the blow off operation.
A need still exists for fluid dispenser arrangements that will ensure that residual material is cleaned off of dispenser nozzles as part of each dispensing cycle so that the amount of food dispensed from one filling cycle to the next does not vary. Further, there is a need for a solution to the nozzle clinging/dripping problem that does not require fundamental design changes in the dispensers.